I. Technical Field
The present invention generally relates to discrete electronic circuit elements, and more particularly, to a composite multilayer capacitive device fabricated via multilayer ceramic (MLC) technology.
II. Related Art
For many years, the fabrication of discrete electronic multilayer capacitors has remained much the same. Generally, layers of conductive metallic electrodes are interleaved with layers of a dielectric ceramic material to form the main capacitor body of a multilayer ceramic capacitor. A termination, or a conductive contact, is disposed at each end of the capacitor body. Moreover, each termination is connected to an exclusive set of alternate electrodes. In effect, the capacitor body responds like a group of capacitors connected in electrical parallel. The parallel connection is effectuated by the common termination interfacing alternate electrodes. The degree of capacitance achieved is a function of the number of interleaved layers, the geometric area of each electrode, and the dielectric constant and thickness of the ceramic layers.
The historical fabrication of multilayer ceramic capacitors and some of the most recently developed methods for manufacturing the same are described in, for example, Wada et al. U.S. Pat. No. 5,046,236 and Kitahara U.S. Pat. No. 4,835,656, both of which are incorporated herein by reference as if set forth in full hereinafter. In general, the fabrication of the capacitor body is a lamination process. A ceramic sheet is obtained in green form. A thick film of a metallic electrode paste is screen printed on the ceramic sheet. Next, the ceramic sheets are stacked, pressed, cut, and then sintered in a kiln. Finally, the terminations are disposed at each end of the capacitor body by a conventional dipping process wherein the capacitor body is dipped into a liquified metallic solution, such as silver, and then sintered in a kiln. Afterwards, the terminations may be plated by one or more other metallic layers, such as a nickel and/or tin plating layer, if desired.
To further enhance the quality of multilayer ceramic capacitors, Berghout et al. U.S. Pat. No. 4,910,638 teaches the implementation of a conductive barrier layer between the capacitor body and the terminations so as to prevent undesirable diffusion of silver from the terminations into the electrodes. Furthermore, Galvagni U.S. Pat. No. 5,072,329 describes a method for multilayer ceramic capacitor fabrication which results in a capacitor resistant to undesirable delamination.
Because multilayer ceramic technology is inexpensive and can be utilized easily for mass production, attempts have been made to incorporate other circuit elements with capacitors using the multilayer ceramic technology. In the art, inductors and capacitors have been laminated alternately to form a single composite device whereby a filter function (high frequency noise absorption function) is obtained. Another composite electronic component is described in Azumi et al. U.S. Pat. No. 5,034,709. In Azumi, a varistor and filter function are implemented in a single composite electronic component using multilayer ceramic technology.
Oftentimes, a need exists in the electronic and computer fields for a series connection of a capacitor and resistor. A series connection of a capacitor and a resistor is required, for example, for matching bus impedances, for data bus terminators adapted to minimize reflections in computer architectures, for digital-to-analog (D/A) and analog-to-digital (A/D) interface circuits, and for central processing unit (CPU) circuits. However, to date, neither prominent researchers nor manufacturers in the art have developed or suggested a technique for fabricating a series connection of a capacitor and a resistor in a single composite electronic component using multilayer ceramic technology. It is known that some manufacturers have created a series connection between a capacitor and a resistor in a unitary device by fabricating a distinct resistor with two terminations adjacent to a distinct capacitor with two other terminations, and then the circuit elements are coupled via connecting a termination from each. Another known technique involves bonding a thick film resistor to an existing capacitor body. However, such configurations are undesirable in that they are costly, occupy valuable space, and can be unreliable due to the increased number of electrical connections (e.g., solder joints).